To comply with OBDII legislation in the United States, all exhaust-relevant components of a motor vehicle must be diagnosed by a device, a so-called control unit, which regulates or controls an internal combustion engine.
The engine fan must also be diagnosed if it is used for diagnosing an exhaust-relevant component of a motor vehicle. Certain methods of diagnosing fans are conventional. In many approaches, the cooling power of the fan is evaluated by a temperature sensor. Other methods use rotational speed sensors to monitor the rotational motion of the fan.
These additional sensors require additional lines in the cable harness of the vehicle. Furthermore, these additional sensors must themselves be diagnosed for compliance with OBDII legislation.